baking normal from high poly to low poly made with instantmeshes issue
The issue is within the exported low poly mesh,
Instant meshes generates sharp edges and custom split normals data to the new generated mesh.

The solution is simple:
In edit mode select all edges and click Ctrl+E and select clear sharp. If that doesn't smooth the object you can click the 'clear custom split normals data'  in the object data properties under geometry data.
Don't forget to check autosmooth angle and shade smooth/flat.

Hope it helps.